The FS1R is the pinnacle of Yamahas FM synthesis with algos holding up to 8 (!) operators at once. In addition you have Formant synthesis that you can blend in with the classic FM and these sounds can be setup into 4 different parts with traditional, albeit digital, filters, amps, LFOs and whatnot.
It can even import original DX7 sysex.
The result can be spectacular, As I demonstrate in this video.

The module flopped back in '98 and was produced for only just over a year and quickly went into the digital purgatory. But over the years to come, rumors began spreading about this other-wordly sound module and now it's highly sought after. As it should be!